The invention relates to field of aircraft terrain advisory systems and more particularly to such systems that provide a cockpit display of terrain.
Various systems have been developed that provide warnings and advisory indications of hazardous flight conditions. Among such systems are systems generally known as ground proximity warning systems (GPWS) which monitor the flight conditions of an aircraft and provide a warning if flight conditions are such that inadvertent contact with terrain is imminent. Among the flight conditions normally monitored by such systems are radio altitude and rate, barometric altitude and rate, air speed, flap and gear positions. These parameters are monitored and an advisory signal and/or warning signal is generated when the relationship between the parameters is such that terrain impact is likely to occur. Typical examples of such systems are disclosed in U.S. Pat. Nos. 3,715,718; 3,936,796; 3,958,218; 3,944,968; 3,947,808; 3,947,810; 3,934,221; 3,958,219; 3,925,751; 3,934,222; 4,060,793; 4,030,065; 4,215,334; and 4,319,218, all assigned to the same assignee as the assignee of the present invention and hereby incorporated by reference.
While the above-referenced systems do provide advisory and warning signals in the event of proximity to terrain, the warnings generated by such systems are based solely upon flight conditions of the aircraft and do not provide any navigational information nor a visual indication of the terrain below the aircraft. Consequently, the sensitivity of such systems must be adjusted to provide adequate warnings when a hazardous flight condition exists without generating false or spurious warnings. However, such an adjustment can result in a compromise that may still result in nuisance warnings over terrain unique to particular geographic areas and shorter than desired warning times in yet other geographic areas.
Several attempts have been made to improve upon such ground proximity warning systems utilizing ground-based navigational information. For example, U.S. Pat. Nos. 4,567,483; 4,646,244; 4,675,823; and 4,914,436 all disclose ground proximity warning systems which monitor the position of the aircraft relative to stored terrain data in order to provide modified ground proximity warnings. However, the utility of such systems is limited. For example, the systems disclosed in U.S. Pat. Nos. 4,567,483 and 4,914,436 disclose ground proximity warning systems which utilize navigational data to modify predetermined warning envelopes surrounding certain particular airports. U.S. Pat. Nos. 4,646,244 and 4,675,823 disclose terrain advisory systems which utilize various ground-based navigational inputs and stored terrain data to provide various ground proximity warning systems based on the position of the aircraft. However, as with the systems described above, none of these systems provide the pilot with navigational information or an indication of the terrain below the aircraft.
Recently, an enhanced ground proximity warning system (EGPWS) which includes a terrain advisory and warning system has been developed. In this system data stored in a terrain data base is used in conjunction with aircraft position information to generate a visual terrain advisories and warning on a cockpit display, such as weather radar. An object of the EGPWS is to provide the crew with a terrain awareness system which provides increased warning times to the pilot of an aircraft of a hazardous flight condition while minimizing nuisance warnings. An example of a EGPWS is described in U.S. patent application Ser. No. 08/509,642 filed on Jul. 31, 1995 and which is assigned to the assignee of this application. However, the terrain display feature of the EGPWS provides at best only a simple contoured display of terrain relative to the altitude of the aircraft. Further, when the aircraft is more than 2000 feet above the highest terrain within the range of the display, no terrain features are shown.
However, there are some circumstances in which it would be desirable to provide the pilots with a contoured display of terrain below the aircraft when the aircraft is not in an immediate hazard condition. Another recent invention claimed in U.S. application Ser. No. 08/902,769 filed Jul. 30, 1997 entitled xe2x80x9cAircraft Information Systemxe2x80x9d provides the flight crew with a means of assessing the potential terrain conflicts which might occur if a rapid descent is initiated from the aircraft""s normal flight path. A loss of cabin pressure, for instance, might require the crew to initiate an emergency decent and it would be very useful if the crew had a map of the terrain below the aircraft. This is particularly important when the aircraft is traversing mountainous terrain. Since the terrain display of the EGPWS normally does not display terrain more than 2000 feet below the aircraft this system is not normally available for planning a rapid decent from a relatively high altitude.
The most recent patents and patent applications provide a LOOK-AHEAD warning generator that generates both a terrain advisory signal and a terrain warning signal based upon the position and trajectory of the aircraft relative to stored terrain data. There are two aspects of the terrain advisory and terrain warning signals: LOOK-AHEAD distance/direction; and terrain threat boundaries. The LOOK-AHEAD distance/direction function detects threatening terrain along the groundtrack of the aircraft. In order to prevent nuisance warnings, the LOOK-AHEAD distance is limited to a specified distance ahead of the aircraft""s current position. Otherwise, potentially threatening terrain along the current flight path of the aircraft relatively far from its current position could produce nuisance warnings.
The terrain threat boundaries are provided along the groundtrack of the aircraft and include a terrain floor boundary, terrain advisory boundaries (yellow alert), and terrain warning boundaries (red alert). The terrain floor boundary is the basis for the terrain threat boundaries and relates to a distance xcex94H below the aircraft proportional to the distance to the closest runway to prevent nuisance warnings when the aircraft is taking off and landing, while providing adequate protection in other modes of operation. Terrain advisory boundaries (yellow alert) are based upon the relationship between the flight path angle xcex3 and a first configurable datum.
The terrain warning boundaries (red alert) generally indicate to the pilot of an aircraft conditions when evasive action is required to avoid terrain contact. The terrain warning boundaries are based on the relationship of the flight path angle xcex3 of the aircraft relative to a second configurable datum. According to current aircraft terrain information systems, the second configurable datum is selected with a fixed upslope of, for example, 6 degrees, which is equal to the average all engines climb capability of modem air transport category aircraft. To date, the datum has failed to take into consideration aircraft type, configuration, altitude and time for takeoff, or other factors. By failing to provide modifications to the configurable datum, no additional alerting time is possible for those situations in which the aircraft is unable to obtain a 6 degree climb gradient due to, for example, loss of an engine. Also, failure to provide modifications to the configurable datum increases nuisance warnings in situations in which the aircraft is carrying less than its full cargo capacity or its full complement of fuel such that the aircraft is able to exceed the nominal 6 degree climb gradient. Thus, a need exists for a real-time estimation of the available climb performance of the aircraft to inform the aircraft terrain information system in those situations in which the nominal 6 degree climb gradient either cannot be obtained or can be exceeded.
The present invention overcomes the limitations of the prior art by providing a real-time estimation of the available climb performance of the aircraft to inform the aircraft terrain information system in those situations in which the nominal 6 degree climb gradient either cannot be obtained or can be exceeded. The invention thereby provides an enhanced terrain advisory and warning system providing reduced nuisance warnings in situations where greater climb gradients can be achieved, while providing extended look-ahead distances in situations where the achievable climb gradient is reduced, for example, by extremely heavy cargoes or engine out emergencies.
According to one aspect of the present invention, a terrain awareness system having enhanced warning times to the pilot of an aircraft of a hazardous flight condition tailored to the real-time estimated climb gradient achievable by the aircraft while minimizing nuisance warnings is provided. Accordingly, the warning time is a function of the real-time estimated climb gradient achievable by the aircraft.
According to another aspect of the invention, the present invention provides a system providing LOOK-AHEAD/LOOK-DOWN as well as LOOK-UP terrain advisory and warning indications to the pilot of an aircraft of a hazardous flight condition based upon the predicted trajectory of an aircraft.
According to still another aspect of the invention, the present invention provides a terrain awareness system that utilizes inputs from a satellite-based navigation system, such as the global positioning system (GPS) and a real-time estimated achievable climb gradient using the parameters of aircraft thrust, weight, drag and lift. Preferably, the aircraft parameters are updated continuously to reflect real-time aircraft achievable climb gradient.
Briefly, the present invention relates to a terrain awareness system (TAS) that provides LOOK-AHEAD/LOOK-DOWN as well as LOOK-UP terrain advisory and warning indications to the pilot of an aircraft of a hazardous flight condition. The TAS includes an airport data base as well as a terrain data base that is structured to provide various resolutions depending on the topography of the particular geographic area of interest. Navigational data from a satellite-based navigation system, such as the global positioning system (GPS), is used to provide a LOOK-AHEAD/LOOK-DOWN and LOOK-UP terrain advisory and terrain warning indications based upon the current position and projected flight path of the aircraft. The terrain warning indications are enhanced using a real-time estimate of the aircraft""s climb capability, such that extended look-ahead distances are provided in situations where the achievable climb gradient is reduced and nuisance warnings are minimized in situations where greater than nominal climb gradients can be achieved.